This project is constituted to isolate 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) from ovine and bovine fetal erythrocytes. The enzyme 20alpha-HSD is involved in progresterone metabolism and may therefore influence the course of pregnancy in these species. Steroid binding at active site of 20alpha-HSD will be studied with a series of synthetic steroids (bromoacetoxyprogesterones) which have been earlier synthesized in this laboratory and proven to be useful for this purpose in connection with the enzyme 3alpha, 20Beta-hydroxysteroid dehydrogenase (E.C.1.1.1.53). Also, a new series of steroid-albumin conjugates, which were found to bind to appropriate uterine receptor proteins, will be tested for biological activity in female rats to gain further insight into the mechanism of steroid hormone action. Taken together, these studies are expected to provide insight into the relationship between specific steroid-macromolecular interactions and the biological activity of sex steroid hormones.